1. Field of the Invention
The invention is in the field of industrial burners, combustors and incinerators and, more particularly, relates to new industrial burners and/or combustors for combustion of either gaseous or particulate fuels including smoke.
Particulate fuels may be wet or dry sawdust and many types of varying moisture content biomass fuels including, agricultural products, wood waste, bagasse, poultry waste, and other cellulosic materials, and especially in the wood products manufacturing or processing operations. Gaseous fuels may mean (gases traditionally used as fuels or they may mean so-called off-gases, including smoke or other combustible gases produced by processes relating to such wood products and other gases, such as from kilns or primary burners, including industrial off-gases. Burners of the invention provide high efficiency. Specifically they may operate with high turndown ratios and high heat release ratios. As used herein, the term off-gases connotes gases produced not primarily as fuels but instead those produced by other processes and apparatus, including gases produced by burners whether of the present invention or other types.
2. Related Art
In the general field of burners, combustors and incinerators for industrial purposes there are myriad different configurations, wherein there has for many years been an increasing focus on efficiency and output. Thus, there have been proposals for swirling or cyclonic combustion and combustion chambers of unusual geometries, as well as many proposals for controlling the entry of air and fuel into the combustion chamber for contributing to swirling or other patterns of combustion motion. There have been various burners proposed for burning, as feed stocks, organics or biomass materials, including so-called green (high moisture content) sawdust, solid cellulosic or wood-containing waste, waste wood, and fragments of wood, and all of which may herein be referred to as wood products. And, burners of various configurations and capabilities have been proposed for combustion of off-gases.
In burners useful for burning such materials, there has been insufficient emphasis on achieving efficiency and flexibility which can result from achieving a high turndown ratio (which may for convenience be abbreviated xe2x80x9cTDRxe2x80x9d), which is the maximum firing rate of the burner divided by the minimum firing rate of the burner. Prior constructions have not achieved sufficiently high TDRs.
The provision of a high TDR burner, or a combustor and burner combination, capable of carrying out combustion of wood products is highly desirable, as such a burner would be capable of being operated over a great dynamic range. If, for example, in a manufacturing or materials handling operation which creates such wood products, which are to be combusted (as for heating or energy extraction for other processes or purposes), the use of a burner having a limited TDR can require that burner operation be terminated if wood product supply rates are insufficient to achieve the minimum firing rate of the burner. Or, if combustion of wood products at low feed rates is to be carried out, an auxiliary fuel such as natural gas, liquefied petroleum (LP) gas, propane, or fuel oil, may have to be fed into the burner for maintaining combustion. But, on the other hand, if the burner is designed for burning wood products at low feed rates, its output may be insufficient to handle high feed rates when wood products to be combusted are being produced at high volumes. Further, if TDR can be increased, much less auxiliary fuel will be required to initiate burner operation.
As an example, in a wood products manufacturing or processing operations, very substantial quantities of green sawdust are created during sawing, planing, shaping, etc., but the rate of production of sawdust will be dependent upon the various wood-handling processes, which vary in rate, time of operation, and volume, so that sawdust may be produced at a highly variable rate.
If the sawdust is to be combusted by a burner for the purpose of extracting heat for other uses (such as heating, boiler operation, drying, etc.), the use of a burner having a high TDR enables its operation on continuous basis or at least for longer periods of operation, as desired.
In the wood products industry, as including also the production of charcoal, there is a need also for dealing with smoke and other gases produced during operations. For example, in cooperage operations where barrels are produced for aging of beverages, such as wines or brandies, etc., some types of barrels require that they be charred, as for the aging of various kinds of whiskeys. Charring operations produce smoke which may need to be combusted. So also, in charcoal kilns, the off-gases are sources of environmental pollution, and may also need to be combusted, i.e., by oxygenation combustion.
It would be desirable to combine a burner, capable of burning wood products for the above-noted purposes, with features for combustion of off-gases in the wood products industry.
Present burners and combustors in the wood products industries have not met the needs for these kinds of combustion, and have not achieved satisfactory TDR and efficiencies for acceptable usage in the wood products industries.
As used for combustion of gases, constructions and methods of the presently claimed invention are of special utility and suitability for burning off-gases such as smoke in situations where other processes and apparatus have produced gases which are amenable to further combustion and which may be rendered less noxious or may be converted to a safer state or destroyed by being burned at relatively high temperatures.
For example, when wood products are charred as in making barrels, smoke may be released which advantageously can be burned.
As a further example, in making charcoal involving partial combustion of wood and other cellulosic or organic substances, including vegetable-based materials smoke may be released from charcoal kilns.
The present invention specifically includes improved gas combustors of high utility in wood products industries and charcoal production.
Accordingly, the present invention provides various combustors and burner-combustor embodiments for burning particulate fuel such as so-called green (high moisture content) sawdust, various feed stocks, organics or biomass materials, including solid cellulosic or wood-containing waste, waste wood, and fragments of wood, and all of which may herein be referred to as wood products or particulate organic fuels or materials.
The invention is also concerned with such burners and combustors which are capable of combustion of gases, such as off-gases produced in the wood products industry, or other gases which are to be oxygenated or burned for conversion to a condition environmentally non-polluting.
Burners and combustors of the present invention achieve high efficiency and flexibility, particularly achieving a very high TDR.
The inventive burners and burner-combustor combinations specifically achieve a high TDR while carrying out combustion of wood products. Burners and combustors of the invention are capable of being operated over a great dynamic range.
The new burners and combustors are especially useful in wood products manufacturing or processing operations, such as stave and barrel-forming (cooperage) operations which create very substantial quantities of green sawdust.
The new burners and combustors, because of their high TDR, efficiency and dynamic range, can be used in operation on continuous basis or for longer periods of operation, and at greatly variable output different as may be desired.
The new burners and combustors disclosed are capable of combustion of a high-moisture, low-Btu value fuels not only providing high TDR but also achieving a high heat release ratio, meaning heat output per volume per unit of time. This allows a smaller size burner or combustor of the present invention than otherwise would be required in a prior art burner, and so the invention results in a burner or combustor of lower cost than heretofore.
Another feature of the presently inventive burners and combustors is the capability for designing them to a desired scale, as according to the intended mode of usage and industry segment in which the burners and combustors will serve. Thus, they are easily scalable.
A further advantage of the inventive burners and combustors is their use of electronic controls using programmable logic controllers, for achieving precise, efficient, safe and reliable control and operation in all modes of usage.
Yet another feature of the invention is a gas combustor especially suited for combustion of smoke and various combustible gases, including off-gases in the wood products industry, such as for example gases produced during cooperage operations and gases produced during the operation of charcoal kilns, as well as other industrial off-gases.
The presently inventive burners and combustors achieve satisfactory TDR and efficiencies for acceptable usage in the wood products industries.
In addition, burners and combustors of the present invention are economical in construction and operation and are easily installed and operated.
The present invention specifically includes improved burner and combustor constructions and methods to provide gas combustors of high utility in wood products industries and charcoal production, as for burning smoke and other gases when wood products are charred as in making barrels, and in charcoal production.
Briefly, the present invention relates to various burner and combustor configurations. Each burner and combustors of the disclosure exhibits a high TDR for combustion of a principal fuel. Each of the proposed burners includes, or comprises, consists of, or consist essentially of, a housing defining an upright combustion chamber lined with refractory material and generally circular in horizontal section, a main combustion region within an upper extent the combustion chamber, an initial combustion zone at a lower end of the combustion chamber of reduced-size cross-section compared to the combustion chamber, a transition region within the combustion chamber increasing in cross-section from the initial combustion zone to the main combustion region, a ceiling of the combustion chamber, a principal fuel feed to supply particulate fuel with combustion air to the initial combustion region, and an auxiliary fuel feed to supply ignition fuel to the initial combustion region for igniting the principal fuel. Multiple sets of tuyeres are provided for controllably introducing combustion air tangentially regions of the combustion chamber for contributing to cyclonic combustion flow in such a manner as to increase diameter of combustion upwardly within the combustion chamber. A counterflow arrangement disrupts cyclonic flow near the ceiling. The ceiling defines an exit for providing escape from the combustion chamber of exhaust gases resulting from combustion in the combustion chamber. The arrangement is such that the principal fuel is ignited in the initial combustion region, and burns with cyclonic flow extending upwardly through the transition region with increasingly greater combustion diameter into the combustion chamber. Various ignition and control features are also disclosed.
Each of the new type of high TDR burners maybe combined synergistically with a smoke or combustible gas combustor mounted to or connected to the burner for receiving hot combustion exhaust gases of 1,600 degrees F. or greater, which exit into a preheat tube located within a smoke-combustor heating chamber. Smoke or other combustible gases such as off-gases from another process enter the heating chamber through gas tuyeres tangential to walls of the heating chamber. The smoke or gaseous combustibles are heated by the preheat tube. The combustor includes a venturi which creates a negative pressure in the heating chamber for drawing the combustible gases from the heating chamber and from the combustible gas tuyeres. Controlled high-velocity air is forced through the venturi tuyeres, causing the venturi action. Controlling the amount of high-velocity air forced into the venturi tuyeres and the cyclonic tuyeres regulates negative pressure created by the venturi. The high-velocity air also serves as combustion air for ignition of the combustible smoke or gases. More combustion air is forced into the top of the venturi chamber through cyclonic tuyeres, enhancing mixing of the air and combustible gases and causing the gases to burn in a cyclonic pattern in the combustion chamber of the combustor. The combustor can be operated to maintain proper negative pressure for optimum draft control while maintaining the correct amount of air and temperature for combustion of the combustible gases in the combustion chamber.
One configuration of smoke combustor disclosed includes a housing configured for receiving the heated exhaust gases from the burner, the housing defining a combustible gas heating chamber including coaxial inner and outer combustion chambers, one or more inlet tuyeres connected to the inner combustion chamber for introducing combustible smoke or other gases to be burned into the inner combustion chamber at one end thereof with cyclonic flow, means for mixing combustion air with said combustible smoke or other gases to form a combustion gas stream moving through the inner combustion chamber with cyclonic movement, a preheat tube within the combustible gas heating chamber into which the heated exhaust gases are ducted for preheating, the preheat tube being of substantial thermal mass and communicating with the inner combustion chamber exit through a plurality of apertures for controlled flow of said heated exhaust gases into the gas stream for preheating the combustible gas stream by mixing the exhaust gases with the stream of air and combustible gases for combustion thereof to provide combustion gases, means at an opposite end of the inner combustion chamber for redirecting counterflow movement of said combustion gases from the inner combustion chamber to the outer combustion chamber for counterflow of combustion gases therein relative to the inner combustion chamber, whereby combustion gases thence travel though the outer combustion chamber along a separating wall which separates the inner and outer combustion chambers, the outer combustion chamber including means for causing continued cyclonic movement of the combustion flow in the outer combustion chamber, and an outlet at an end of the outer combustion chamber remote from the redirection means for delivery of completely burned combustion gases.
Other objects and features will be in part apparent and in part pointed out below.